首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   500735篇
  免费   56710篇
  国内免费   769篇
  558214篇
  2021年   4371篇
  2018年   5115篇
  2017年   4826篇
  2016年   7106篇
  2015年   10542篇
  2014年   12166篇
  2013年   15967篇
  2012年   19270篇
  2011年   19641篇
  2010年   12918篇
  2009年   11758篇
  2008年   17053篇
  2007年   17472篇
  2006年   16458篇
  2005年   15734篇
  2004年   15704篇
  2003年   14620篇
  2002年   14160篇
  2001年   19668篇
  2000年   19462篇
  1999年   15777篇
  1998年   6396篇
  1997年   6165篇
  1996年   5825篇
  1995年   5567篇
  1994年   5305篇
  1993年   5295篇
  1992年   13005篇
  1991年   12868篇
  1990年   12602篇
  1989年   12082篇
  1988年   11210篇
  1987年   10554篇
  1986年   10093篇
  1985年   9819篇
  1984年   8251篇
  1983年   7168篇
  1982年   5494篇
  1981年   4948篇
  1980年   4655篇
  1979年   7614篇
  1978年   6216篇
  1977年   5542篇
  1976年   5195篇
  1975年   5955篇
  1974年   6511篇
  1973年   6309篇
  1972年   5586篇
  1971年   5212篇
  1970年   4403篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
Horse serum albumin has been shown to meet the requirements to protein preparations for microanalysis and thus to be suitable for use in kits of reagents for the radioimmunological determination of insulin and myoglobin, for the determination of tick-borne encephalitis virus antigen by the method of the enzyme immunoassay and for the stabilization of proteins in the hemagglutination test and the hemagglutination inhibition test.  相似文献   
942.
Identification of the protein HC receptor   总被引:2,自引:0,他引:2  
In the present study, we demonstrate for the first time the presence of a specific receptor for protein HC on the surface of human cells using the human histiocytic lymphoma cell line U937. Cells treated for 4 days with the maturation inducer phorbol 12-myristate 13-acetate, were found to increase both the number of cells binding protein HC (76% higher than for untreated cells) and the expression of protein HC receptors. Protein HC bound to these cells in a specific and saturable manner. Scatchard analysis at 4 degrees C, using radioiodinated protein HC, indicated a single class of low-affinity receptor (Ka = 2-5 x 10(7) M-1) and 20,000-30,000 receptors per cell. Monoclonal antibodies against protein HC abrogated specific binding of this protein to U937. In contrast, monoclonal antibodies that did not react with protein HC (anti-LFA-1 alpha, anti-MO1 alpha) were without effect on the binding reaction.  相似文献   
943.
Summary. Blood samples from a female sheep-goat hybrid and its back-cross male offspring were tested for electrophoretic variants of plasma albumin, transferrin and esterase, and of red cell carbonic anhydrase, nucleoside phosphorylase, NADH-diaphorase, 'X'-protein, superoxide dismutase, malic enzyme and haemoglobin. Red cells were also tested for blood group antigens. Both animals showed variants that could not be attributed to either sheep or goat alone, thus confirming previous chromosomal data that the female was a genuine sheep-goat hybrid.  相似文献   
944.
Fertilizer application to rice-fields in the river-deltas in the Mediterranean area is a potential menace for wildlife protection, through eutrophication.Fertilizer use shows a trend of increasing rates of N application. A rate for N of 200 kg ha–1 has become normal and a rate of 400 kg ha–1 has already been recorded.Denitrification causes large losses of N with the result that more fertilizer is applied. This is especially true for the Camargue (S-France), where N is applied long before the rice (Aryza sativa) can take it up.Therefore we have tried to develop techniques which need the application of smaller amounts of N which are used more efficiently. In order to do this we tried to establish a N budget for rice-fields.Experiments were therefore set up in the field (plots of 550 m2) and in pots (2–3 l). Our results suggest that a late application of N (e.g. when the rice shows signs of N-deficiency by becoming yellowish), but at lower concentrations (70 kg ha–1) can produce the same ultimate yield. The introduction of carp without any further input of N produced the same final yield.The N budget shows that 15±1.5 g m–2 of N is needed for a normal crop. N losses due to denitrification may be as high as 12.2–13.6 g m–2 of N. The input by irrigation water may provide up to about 20% of the input; N fixation is negligible. We estimate that 25–50% of the N missing in the budget comes from minderalization of the organic N pool in the soil. Denitrification may render part of this pool bio-available by oxidation. In sum, this work has revealed some surprising effects with potentially important consequences for farming practice and, in consequence, for conservation.  相似文献   
945.
A kinin-directed monoclonal antibody to kininogens has been developed by the fusion of murine myeloma cells with mouse splenocytes immunized with bradykinin-conjugated hemocyanin. The hybrid cells were screened by an enzyme-linked immunosorbent assay (ELISA) and a radioimmunoassay (RIA) for the secretion of antibodies to bradykinin. Ascitic fluids were produced and purified by a bradykinin-agarose affinity column. The monoclonal antibody (IgG1) bound to bradykinin, Lys-bradykinin, Met-Lys-bradykinin, and kininogens in ELISA. Further, this target-directed monoclonal antibody recognized purified low and high molecular weight bovine, human, or rat kininogens and T-kininogen in Western blotting. After turpentine-induced acute inflammation, rat kininogen levels increased dramatically in liver and serum as well as in the perfused pituitary, heart, lung, kidney, thymus, and other tissues, as identified by the kinin-directed kininogen antibody in Western blot analyses. The results were confirmed by measuring kinin equivalents of kininogens with a kinin RIA. During an induced inflammatory response, rat kininogens were localized immunohistochemically with the kinin-directed monoclonal antibody in parenchymal cells of liver, in acinar cells and some granular convoluted tubules of submandibular gland, and in the collecting tubules of kidney. Northern and cytoplasmic dot blot analyses using a kinin oligonucleotide probe showed that kininogen mRNA levels in liver but not in other tissues increase after turpentine-induced inflammation. The results indicated that rat kininogens are distributed in various tissues in addition to liver and only liver kininogen is induced by acute inflammation. The target-directed kininogen monoclonal antibody is a useful reagent for studying the structure, localization, and function of kininogens or any protein molecule containing the kinin moiety.  相似文献   
946.
947.
948.
949.
950.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号